[ALSA] ice1712 - Fix wrong register value for DMX 6FIRE

I have just discovered I made an error in the register value set in 'Limit
dmx6fire to 6 dacs' patch (bug1472).  The value set should be '2a' not '0a'
as in the original patch, which unintentionally disables the 2nd MPU 401
UART.

Signed-off-by: Alan Horstmann <gineera@aspect135.co.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>